Polymers of monoethylenically unsaturated dicarboxylic acids, monoethylenically unsaturated monocarboxylic acids, and carboxyl-free monoethylenically unsaturated monomers having weight average molecular weights (Mw) less than 30,000 are useful as scale inhibitors, deflocculants, dispersants, in water circulating systems and as encrustation inhibitors, builders, anti-filming agents, sequestering agents, and dispersants in detergents and cleaning formulations.
A well known problem in preparing these polymers is that it is difficult to control the molecular weight and degree of branching during the preparation of these polymers. The control of molecular weight is especially difficult when preparing polymers containing low levels of monoethylenically unsaturated dicarboxylic acids of from about 3 to about 50 weight percent. Another problem associated with preparing these polymers is that it is difficult to achieve low residual levels of monomer in the polymer product, preferably less than 3.0 weight percent based on the weight of the polymer product.
One solution to controlling the molecular weight of the polymer is disclosed in U.S. Pat. No. 5,100,980 to Hughes et al., hereinafter referred to as "'980 patent." The '980 patent discloses a process for preparing copolymers containing from about 3 to about 25 weight percent monoethylenically unsaturated dicarboxylic acids and 75 to about 97 weight percent monoethylenically unsaturated monocarboxylic acids having a Mw less than 25,000. The process described in the '980 patent requires the monomers to be polymerized in the presence of a polymerization initiator, copper salt polymerization moderator, and neutralizer. The presence of the copper salt moderator in the '980 patent is believed to promote high conversion of the monomers and control the molecular weight of the resulting copolymers.
U.S. Pat. No. 5,244,988 also to Hughes, et al., hereinafter referred to as the "'988 Patent," discloses another process for making low molecular weight copolymers of ethylenically unsaturated dicarboxylic acid monomers. The copolymers in the '988 patent are produced by cofeeding the monomers and a neutralizer in the presence of a metal salt activator. The copolymers produced have molecular weights ranging from about 1000 to about 100,000 and the cofeeding of the monomers is believed to produce a copolymer of more uniform composition.
However, the processes disclosed in the '980 and '988 patents produce a copolymer which is completely or partially neutralized. It may be desirable in some applications for performance or cost reasons to directly produce a polymer product which is not neutralized. Additionally, the '988 and '980 patents produce a polymer product which is colored dark yellow to brown due to the processing conditions.
Therefore, it is an aim of this invention to produce polymers formed from 3 to 50 weight percent monoethylenically unsaturated dicarboxylic acids, and 50 to 97 weight percent monoethylenically unsaturated monocarboxylic acids having weight average molecular weights less than 30,000 without using a neutralizer.
It is also an aim of this invention to provide a process for making polymers formed from monoethylenically unsaturated dicarboxylic acids and monoethylenically unsaturated monocarboxylic acids where the resulting polymer product has low color.
It is also an aim of this invention to produce polymers formed from monoethylenically unsaturated dicarboxylic acids and monoethylenically unsaturated monocarboxylic acids having comparable or improved performance over polymers currently in use.